Achieving Sustainable Phosphorus Use in Food Systems ... - MDPI

sustainability Article

Achieving Sustainable Phosphorus Use in Food Systems through Circularisation Paul J. A. Withers 1, * 1 2 3

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, Donnacha G. Doody 2 and Roger Sylvester-Bradley 3

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Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK Agri-Food and Biosciences Institute, Belfast BT9 5BX, UK; [email protected] ADAS, Boxworth, Boxworth, Cambridge CB23 4NN, UK; [email protected] Correspondence: [email protected]; Tel.: +44-1524-595581

Received: 8 April 2018; Accepted: 28 May 2018; Published: 30 May 2018

Abstract: The notion of a phosphorus (P) circular economy provides the philosophy, framework, and opportunity to enable food production systems to become more efficient, sustainable, and resilient to a future P scarcity or sudden price shock. Whilst P recovery and recycling are central strategies for closing the P cycle, additional gains in environmental performance of food systems can be obtained by further minimising the amounts of P (a) introduced into the food system by lowering system P demand and (b) lost from the system by utilising legacy P stores in the landscape. This minimisation is an important cascading component of circularisation because it reduces the amounts of P circulating in the system, the amounts of P required to be recycled/recovered and the storage of unused P in the landscape, whilst maintaining agricultural output. The potential for circularisation and minimisation depends on regional differences in these P flow dynamics. We consider incremental and transformative management interventions towards P minimisation within circular economies, and how these might be tempered by the need to deliver a range of ecosystem services. These interventions move away from current production philosophies based on risk-averse, insurance-based farming, and current consumption patterns which have little regard for their environmental impact. We argue that a greater focus on P minimisation and circularisation should catalyse different actors and sectors in the food chain to embrace P sustainability and should empower future research needs to provide the confidence for them to do so without sacrificing future regional food security. Keywords: phosphorus; food system; circular economy; circularisation; minimisation; efficiency; resilience; sustainability

1. Introduction The long-term adverse impacts of societal functioning on air, soil and water quality and ecosystem integrity are becoming more and more evident and are a cause of increasing concern for planetary stability and human well-being [1,2]. A major driver of this environmental damage has been the intensification of agriculture to satisfy a growing demand for food and changing dietary patterns, and further degradation is forecast as the population continues to expand and urbanise [3,4]. Depletion of non-renewable resources required for food production, regional imbalance in accessibility to resources required for closing yield gaps, declines in global biodiversity due to land clearing for agriculture, and the confounding effects of climate change are additional pressing issues that society needs to address. Future global food security therefore critically depends on using our natural resources more efficiently and sustainably and simultaneously improving the productivity and environmental management of agricultural land. Doing so may require a radical redesign and

Sustainability 2018, 10, 1804; doi:10.3390/su10061804

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Sustainability 2018, 10, 1804

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fostering of new, more resilient agri-food economies involving all stakeholders (including consumers) and more innovative management of agricultural systems [5–7]. One of the critical resource inputs for securing sustainable food production is phosphorus (P). Alongside other essential inputs such as nitrogen (N) and water, a lack of P availability greatly restricts crop and animal production in many regions, whilst past overuse of P in agriculture in other regions has led to unnecessary soil P accumulation, and widespread P leakage causing endemic aquatic eutrophication and reduced biodiversity [8–10]. This system leakage is much greater than occurs naturally over geological timescales and has become exaggerated by the insurance-based approach to P management that advocates using too much fertiliser rather than too little. Further environmental damage can be anticipated in those regions which have yet to expand their use of reactive P for future food security. Although phosphate rock (PR) is now widely recognised as a finite and price volatile resource of variable quality (see Mew et al. [11] for a recent review), the reactive P produced from PR is still used very inefficiently in the food system [12,13]. Conserving PR resources is therefore of critical importance for future food security, especially for those more vulnerable regions with high P demand and little or no PR reserves of their own. The economic, environmental, and social justification for increasing the efficiency and sustainability of P use in the global food system is therefore very clear. Circular and green economies offer a key philosophical and strategic paradigm to improve the efficiency and sustainability of P use in the food system, not least because of the large opportunities for recovery and recycling of nutrients embedded in the food chain [14,15]. Some vulnerable developed regions with widespread eutrophication (e.g., Europe) are now starting to embrace the circular economy [16], whilst developing regions with more limited access to resources (e.g., to reactive P) and less nutrient demand have been practising circularisation for many years [17,18]. Other regions will perceive the need to continue with the current linear model of food production (i.e., a take-make-waste approach) to maintain economic growth (e.g., Asia, South America) [19,20]. Maximising the environmental performance of a circular economy will also require all actors (producers, processers, retailers, consumers, and regulators) and sectors (e.g., commodities) to take responsibility for delivering the broader sustainability principles (e.g., minimum inputs and zero waste) on which a circular economy was founded [21,22] (for example, the recent adoption of green chemistry in fertiliser P manufacture [23]). This necessitates an interdisciplinary and multi-scale approach to tackling the drivers of unsustainability [24,25], which in the case of P are the policies and practices that generate too much reactive P in the food chain, and its unbalanced distribution across rural and urban landscapes (Figure 1). Making such an all-embracing change requires rapid global acceptance of an essentially incontrovertible old philosophy: circularisation aimed at closing the P cycle. Here we revisit the foundations of circular economies using global P sustainability as our example. Since P cycles span timescales ranging from geological eras to minutes, we consider the typical annual P cycle of a food system. We argue that there should be a greater focus on minimisation within the P circular economy of a food system and that circularisation should actively reduce the amounts of this critical nutrient entering and circulating within the food chain, and in doing so reduce wastage and leakage. Since the circular economy philosophy is still very much in its infancy with respect to its implementation within agriculture, we highlight management opportunities for transformative innovations toward minimisation.


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Figure Figure 1. 1. (A) (A) Inputs Inputs of ofreactive reactive PPin infertilisers fertilisers drive drive the theannual annual surpluses surpluses of of PPthat thatreflect reflect PPinefficiency inefficiency and pollution risk across Europe during 2005–2014. Recent reductions in fertiliser and pollution risk across Europe during 2005–2014. Recent reductions in fertiliser PP use use in in the the EU EU have distribution of have driven driven down down surpluses surpluses to to nearly nearly zero, zero, but but there there is is variation variation in in the the distribution of the the surplus surplus between between countries; countries; (B) (B) The The relative relative contribution contribution of of fertiliser fertiliser and and manure manure PP inputs inputs to to total total crop crop P P demand (ratio 1.0) in different EU countries averaged for the period 2005–2014. Inputs of fertiliser P demand (ratio 1.0) in different EU countries averaged for the period 2005–2014. Inputs of fertiliser could stillstill be reduced in many countries and still demand, if manure P could be recycled P could be reduced in many countries andmeet still crop meetPcrop P demand, if manure P could be and substituted for fertiliser more more effectively. DataData are are Eurostat statistics recycled and substituted for fertiliser effectively. Eurostat statisticsononnutrient nutrient balances balances (http://ec.europa.eu/eurostat/statistics). (http://ec.europa.eu/eurostat/statistics).

2. 2. Minimisation Minimisation of of P P within within the the Circular Circular Economy Economy Developing Developing aa circular circular economy economy for for P P provides provides aa means means to to facilitate facilitate the the transition transition to to greater greater P P sustainability within agriculture by closing the P cycle and adopting P stewardship across sustainability within agriculture by closing the P cycle and adopting P stewardship across multiple multiple scales. scales. For For example, example, Withers Withers et et al. al. [26] [26] proposed proposed aa 5R 5R stewardship stewardship strategy strategy (1R:Realign (1R:Realign PP inputs, inputs, 2R:Reduce P losses, 3R:Recycle P in bio-resources, 4R:Recover P in wastes, and 5R:Redefine P in food 2R:Reduce P losses, 3R:Recycle P in bio-resources, 4R:Recover P in wastes, and 5R:Redefine P in systems) for managing P thatPwould lead to a more resource-efficient, competitive, sustainable and food systems) for managing that would lead to a more resource-efficient, competitive, sustainable healthy society. Circular economies were conceived from a cradle to cradle philosophy which and healthy society. Circular economies were conceived from a cradle to cradle philosophy which considers considers the the life life cycle cycle of of any any system, system, commodity commodity or or product product in in terms terms of of its its use use of of natural natural resources, resources, environmental impact and social impact [16,21,23]. Circular economies are built on the green environmental impact and social impact [16,21,23]. Circular economies are built on the green chemistry chemistry principles of developing environmentally benign production systems that are output principles of developing environmentally benign production systems that are output driven (i.e., use driven (i.e., use the minimum inputs necessary), renewable materials and and embed diversity, the minimum inputs necessary), run-on renewablerun-on materials and embed diversity, which design and which design out waste and reduce losses. They therefore not only envision closed-loop systems out waste and reduce losses. They therefore not only envision closed-loop systems through recycling through recycling and recovery, implicitly work on the principle of in minimisation which, in the and recovery, but implicitly work but on the principle of minimisation which, the context of sustainable context of sustainable P use, requires proactive reductions in the amounts of nutrients introduced into, circulating within and lost from the food chain. Intensive agriculture has evolved into an industry based on the linear economy model with exactly the opposite goals to those of circular economies—for example, in the case of P, agricultural


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P use, requires proactive reductions in the amounts of nutrients introduced into, circulating within and lost from the food chain. Intensive agriculture has evolved into an industry based on the linear economy model with exactly the opposite goals to those of circular economies—for example, in the case of P, agricultural systems are input driven and do not consider end-user P requirements. They are heavily dependent on a non-renewable resource at least in the Anthropocene (i.e., PR), have actively reduced plant diversity in favour of intensive rotations with few crop types, produce copious amounts of bulky waste that is difficult to handle, and cause considerable environmental degradation at significant cost to society [27]. These intensive systems have been driven by short-term economic gains that fuelled the green revolution, and in the case of P, a founding need to build-up soil fertility. Their slow evolution has precipitated traditional beliefs and attitudes centred on insurance-based, risk averse input management that will be hard to change [28]. The more intensive agriculture has become, the more it has moved toward this linear model, and the more P-inefficient it has become. Facilitating a return to a more sustainable circular P economy that focuses on minimisation within agriculture is therefore going to require a radical change in philosophies, attitudes and practices by all actors, and across all sectors, of the food chain from production to consumption [29,30]. Clearly, such minimisation must not jeopardise the economic viability of farming businesses by incurring unacceptable costs, or by reducing agricultural output in the longer term. 3. Managing a P Circular Economy to Promote Minimisation The concept of a circular economy in respect of agriculture, and more specifically P use in agriculture, is in its infancy and is justifiably concentrating on turning waste into a secondary P resource, where the largest opportunity for business development resides [31]. For example, a number of nutrient platforms and action plans have recently emerged to help facilitate industry investment in recovery and recycling technologies and the future development of markets in secondary P resources [32]. Recovering and recycling P inherently helps to close the P cycle by reducing point-source P loss through wastage (e.g., as wastewater effluent), and lowering inputs of primary reactive P through substitution. However, these options increase the amounts of P circulating in the food system (i.e., the sum of all internal P flows), and they do not reduce the surplus P that accumulates in the soil, both of which increase the risk of diffuse-source P loss in land runoff. A circular economy which simply generates secondary resources through recovery and recycling therefore underestimates the potential for economic and environmental gain by further minimising the amounts of P introduced into, and lost from, the food chain. Further gains in the environmental performance of circular P economies are possible by lowering the P demands of the system, the amounts of unused P that need to be recovered and recycled, and those losses associated with P circulating or stored in the food system. Conceptually, the P circular economy can be considered as a closed system, with the boundaries of the system defined by stakeholder needs and perceptions. The spatial scale at which the system operates (e.g., farm, catchment, national, food system and global) determines the quantity of P circulating around the system and the P stored within it (Figure 2). Here, we consider the system boundary to be an annual cycle of the food system, which Cordell and Neset [25] define as a combination of the production and consumption system, both of which include socio-economic (e.g., sectors) and biophysical (e.g., landscape) sub-systems that incorporate human and non-human actors. The food system is fed by P inputs, which are defined by its perceived P demand: at the farm scale this is the anticipated P requirement of crops (crop P offtake) and animals (dietary intake). The P outputs from the food system include P exports related to global trade and market conditions, and P wastage and losses to the environment. For example, losses occur not only as a result of incomplete P recapture at wastewater treatment centres, but also due to landscape release of the P which is circulating (e.g., in manures) and stored (e.g., in soil) at farm scale [33]. The amount of P circulating in the system is driven by the momentum of the system. Momentum is the mass of P in motion, or circulating, in the system dependent on the cropping area, the numbers


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of animals and the number of consumers relying on the food system. This motion is exemplified by the journey added P makes in the food system: fertiliser to soil, soil to crop, crop to animal, crop and animal to food processor, food processor to households, all food system manures returned back to soil. In addition2018, to P,10, system momentum Sustainability x FOR PEER REVIEW is controlled by other inputs (e.g., energy, water, other nutrients), 5 of 16 and consequently, the amount of circulating P cannot be reduced below the minimum P requirement of requirement the system to function, i.e., produce nutritious and stores sufficient food. Thethe stores of P the system to of function, i.e., produce nutritious and sufficient food. The of P represent amounts represent thesurplus amounts surplus P Stores in theofnatural of unused of unused or P inof theunused natural or environment. unusedenvironment. anthropogenicStores P (legacy P) have anthropogenic P (legacy P)in have over time, largely in soils [34], and in addition to built up over time, largely soilsbuilt [34],up and in addition to accessible recycled/recovered P accessible resources, recycled/recovered P resources, resilience against future legacysource soil P confer resilience against future Pconfer shortages. However, legacy soilPPshortages. stores are However, also an endemic stores aretoalso an endemic sourceneed of Ptoloss water, and therefore need to The of P loss water, and therefore be to optimised [35]. The capacity of be theoptimised landscape[35]. to store capacity the landscape to store(termed P without accelerated P leakage (termed catchment buffering P withoutofaccelerated P leakage catchment P buffering capacity [36]) is also anPimportant capacity [36]) is also an importanteutrophication sustainability metric to minimise eutrophication impacts. sustainability metric to minimise impacts.

Figure 2. Conceptual Conceptual representation representation of of PP flows flows in in aa circular circular economy economy based based on inputs, outputs, outputs, and stored storedPPand andthe thepotential potentialimpact impactofof management adaptations and transformations circulating and management adaptations and transformations on on these flows. The size of the arrows reflects the magnitude of the flow which will vary in different these flows. The size of the arrows reflects the magnitude of the flow which will vary regions. A transformed circular economy which embraces full minimization potential has the greatest environmental benefit (lowest inputs and and losses). losses).

A sustainable food P circular circular economy economy must driven by by the the A sustainable food system system based based on on aa P must therefore therefore be be driven minimum momentum of of thethe system; i.e., i.e., cropcrop P, animal dietary P, and minimum PP required requiredfor forthe thecontinued continued momentum system; P, animal dietary P, human dietary P demand. The momentum of the food system is governed by the co-optimisation of and human dietary P demand. The momentum of the food system is governed by the co-optimisation all required resources forfor thethe system to function (i.e.,(i.e., notnot justjust P) and willwill therefore usually exceed the of all required resources system to function P) and therefore usually exceed minimum human dietary P demand that would the minimum human dietary P demand that wouldotherwise otherwisedrive drivesystem systemPP momentum. momentum. The The inputs inputs required to satisfy this minimum demand will depend on the P supplied by P stores in the required to satisfy this minimum demand will depend on the P supplied by P stores in the system, system, the can augment thethe supply of stored P with recycled P, and the synergies synergies in insystem systemmanagement managementwhich which can augment supply of stored P with recycled P, the efficiency with which the different P inputs are utilised. This can be represented by a fundamental equation PI = PD − (PS + PR)/PE

(1)

where PI is the requirement of the food system for reactive P inputs, PD is the P demand of the food


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and the efficiency with which the different P inputs are utilised. This can be represented by a fundamental equation PI = PD − (PS + PR )/PE (1) where PI is the requirement of the food system for reactive P inputs, PD is the P demand of the food system driven by system momentum, PS is the P supplied by the P stores in the food system, PR is the Sustainability 2018, 10, x FOR PEER REVIEW 6 of 16 P recycled in the system, and PE is the efficiency with which PD , PS , and PI are utilised. In highly developed regions, the current food system receives more reactive P than is required, In highly developed regions, the current food system receives more reactive P than is required, circulates and stores more P than it needs with the result that foods are very rich in P and P losses circulates and stores more P than it needs with the result that foods are very rich in P and P losses to to water are relatively high (Figure 2A). In developing regions, total P demand and the amounts water are relatively high (Figure 2A). In developing regions, total P demand and the amounts of P of P circulating in the food system are lower, reflecting restricted yield potential due to limited circulating in the food system are lower, reflecting restricted yield potential due to limited access to access to reactive nutrient inputs, and soil losses due to erosion [37]. Consideration of Equation (1) reactive nutrient inputs, and soil losses due to erosion [37]. Consideration of equation 1 suggests that suggests that management interventions in the food system to facilitate the transition to a P circular management interventions in the food system to facilitate the transition to a P circular economy economy should occur in three strategic ways: managing the P momentum of the system to lower should occur in three strategic ways: managing the P momentum of the system to lower P demand P demand (PD ), maximising potential synergies in the system through P recycling and recovery (PD), maximising potential synergies in the system through P recycling and recovery opportunities opportunities (PR ) and managing the soil P store (PS ) to minimise P losses (Figure 3). Interventions (PR) and managing the soil P store (PS) to minimise P losses (Figure 3). Interventions may encompass may encompass both incremental change (i.e., adaptations to the system) and transformative change both incremental change (i.e., adaptations to the system) and transformative change (system (system transformations) [38,39]. transformations) [38,39].

Figure 3. Three strategic approaches towards minimization in the P circular economy of the food Figure 3. Three strategic approaches towards minimization in the P circular economy of the food system system based on managing system momentum, managing system synergies and managing system based on managing system momentum, managing system synergies and managing system stores. stores. Examples of adaptive (coloured in brown) and transformative (coloured in blue) 5R P Examples of adaptive (coloured in brown) and transformative (coloured in blue) 5R P stewardship stewardship interventions that interface to these three approaches are also shown. The P stewardship interventions that interface to these three approaches are also shown. The P stewardship 5Rs are 5Rs are 1R:Realign P inputs, 2R:Reduce P losses, 3R:Recycle P in bio-resources, 4R:Recover P in 1R:Realign P inputs, 2R:Reduce P losses, 3R:Recycle P in bio-resources, 4R:Recover P in wastes, wastes, and 5R:Redefine P in food systems, [26]). and 5R:Redefine P in food systems, [26]).

Improving the efficiency and sustainability of P in the food system is currently based upon Improving the efficiency and management. sustainability An of Padapted in the food system can is currently basedas upon incremental adaptations to system food system be considered one incremental adaptations to system management. An adapted food system can be considered as one where management has been altered to be more P efficient at the farm scale (e.g., targeted P inputs where management has been altered to be P efficient at the farm scale (e.g., targeted P inputs [40]), [40]), recycling is optimised as much as more possible through integrated farming practices [41], and P recycling is optimised as much as possible through integrated farming practices [41], and P losses are losses are managed by implementation of best management practices [42]. Further benefits to ES managed by implementation of best management practices [42]. closely Furthermatch benefits to ES delivery will delivery will arise by relocating production systems to more land use capability, resource availability and environmental sensitivity [36,43], but essentially the P momentum and demand of an adapted system has not been greatly altered (Figure 2B). In contrast, a transformed system can be considered as one where the P momentum of the system is changed by minimising the P demand of the system for a required output and which would have a cascading effect on the P circulating in, and lost from, the system (Figure 2C). For example, fertiliser and feed P inputs would


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arise by relocating production systems to more closely match land use capability, resource availability and environmental sensitivity [36,43], but essentially the P momentum and demand of an adapted system has not been greatly altered (Figure 2B). In contrast, a transformed system can be considered as one where the P momentum of the system is changed by minimising the P demand of the system for a required output and which would have a cascading effect on the P circulating in, and lost from, the system (Figure 2C). For example, fertiliser and feed P inputs would be lowered to meet the reduced P demand, foods and feeds will then have reduced P contents, and the manures and wastes recycled to land would have lower P content. If their P content is not low enough for return to the land, P would need to be recovered before they are recycled to land. Inherently lower surpluses of P in a transformed system would lead to lower soil P storage, which would both reduce P losses from the system and increase catchment P buffering capacity. 3.1. Changing the Momentum of the System An effective circular economy requires that agricultural systems should be output driven (i.e., pull-system) rather than input driven (i.e., push-system). Fertiliser P and animal feed P supplements have been generously applied in the past to maximise food production potential but with little regard for actual end user P requirements or human dietary demand for P [44]. Fuelled by economic gain, such a push system generates food and feed commodities richer in P than they need to be. In addition to the P embedded in farm produce, P is typically added during processing to enhance the appearance, taste and shelf-life of foods and feeds [45,46]. Consequently, humans and animals in prospering nations have an excess of P in their diets which is surplus to metabolic needs, nutritionally redundant due to chelation of mineral elements (Ca, Mg, Fe, and Zn) by phytate, and may even be harmful to health in some vulnerable people [47,48]. Excess dietary P also leads to higher amounts of P excreted requiring treatment, disposal and/or recycling, which considerably increases the risk of wastage and eventual leakage of P to inland and coastal waters because manures are difficult and costly to manage precisely [19,49]. Given that this excess dietary P is not all useful, and that expensive reactive fertiliser and feed P inputs are generously coupled to crop and animal P demand, lowering the P content of foods seems a logical step towards minimisation of P in the circular economy since it has a positive cascading effect on the amounts of P circulating in the system. Modulating animal diets through precision feeding [50], withholding inorganic P supplements in ruminant diets [51], or substituting phytase for inorganic P in non-ruminant diets [52], regular soil analysis and adopting 4R (right source, rate, time and place [40]) nutrient management on the farm are examples of beneficial incremental adaptations to source P management within crop and animal farming systems. Further adaptations to the human diet by reducing the amount of P additives used during food processing might be anticipated if human health concerns over dietary P excess prove real. Such incremental management changes are based on the principle of avoiding overuse of P by more precisely matching P inputs to actual demand (a 1R P stewardship strategy [26]). However, whilst they will improve P use efficiency often to economic advantage, they do not change the momentum of the system and therefore its functional P demand. An additional and more challenging transformative change to food system momentum is to reduce crop and animal P demand through selective breeding for improved P efficiency. Minimising the P demands of the food chain whilst maintaining yield is economically, environmentally, and socially attractive because it provides a framework for automatically driving lower P inputs, reduces the amounts of P excreted, and is nutritionally beneficial in reduced phytate levels—for example, by lowering the total P and phytate-P content of cereal grain [47,53]. These are essential ingredients for catalysing a circular P economy based on minimisation with benefits for overall P use efficiency, provided crop vigour, yield, and quality are not compromised in the longer term. Lowering P demand could also have a major impact in achieving sustainable intensification in developing countries where the financial resources to purchase P fertilisers are limited [54,55]. Crops and animals demonstrate significant variation in phenotypic traits for soil P acquisition and P utilization depending on their


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environment [56,57], and a number of molecular breeding techniques are available and developing to progress desirable trait enhancement, including the use of gene markers, mutagenesis (e.g., CRISPR technology) and epigenetic inheritance [58–61]. For example, a mutant genotype of barley (Hordeum vulgare L.) with a lpa1−1 allele for low phytic acid generated seed with a 35% reduction in endosperm P and a 15% reduction in total seed P [62]. A transition toward P-efficient crop and animal breeding programmes is currently confounded by a lack of industry desire to define what minimum level of end user P demand is realistic and to accept that P efficiency is a trait worth selecting for. Defining a minimum system P demand is a key first step in redesigning the food system to be more efficient with minimum waste (a 5R P stewardship strategy [26]). In a true circular economy, the minimum dietary P demand by the human population within the food system boundary should drive the P momentum of the system. Although this is not feasible because of the need to co-optimise resources other than P required for the food system to function, dietary choice and in particular the ratio of meat, dairy, and eggs to plant in the human diet has a very large influence on the P momentum of the food system [63,64] and the overall efficiency with which P (and other nutrients) are utilised in the food chain and their environmental impact [65]. This is because animal production systems are inherently more P inefficient than crop production systems, and they require significantly more P inputs to provide the same amount of protein. Shifting to a more plant-based diet would therefore lower system P demand considerably, with positive cascading effects on the P circulating and lost from the food system. For example, Thaler et al. [66] estimated that food system P demand was reduced by 20–25%, and P loss to water was reduced by 5–6%, when the average Austrian diet contained 60% less meat. However, policies to help implement such a transformative societal change as changing human diets are lacking because of the need to productively manage land not suitable for crops, maintain livelihoods of rural communities, and to maintain freedom of consumer choice. This puts the onus on consumers and the stakeholders who have a large influence on consumer behaviour. In reality, global diets are likely to shift toward more P-consuming meat-based diets as developing nations become wealthy and with increasing urbanisation of an expanding population [67]. Changing society’s dietary habits toward more environmentally friendly food choices therefore remains an important challenge for sustainable P management and for optimising minimisation and the environmental performance of circular P economies. 3.2. Managing the Recycling/Recovery Synergies in the System Reuse, recycle, and recovery are traditional R concepts in any circular economy and are key to minimising P inputs to the system [23]. In the context of P, reuse is a redundant R because reactive P immediately changes its state on entering the food system. However, opportunities for reducing P surpluses by recycling and recovery are large because P inputs in fertilisers and manures still exceed current crop P demand in many of the developed countries (Figure 1B). In reality, implementing these opportunities cost-effectively is very challenging due to scale disconnects in nutrient distribution: examples of the current difficulties are the general inaccessibility to manure P on intensive arable farms [68], the excessive amounts of P produced by factory farms with limited land area and associated increased pollution risk [69], and the limited recycling of P from urban areas back to agricultural land [13]. For example, in a small Pennsylvania catchment, Nord and Lanyon [70] found that 20% of the farms accounted for over 80% of N and P flows in the catchment; no crops grown in the catchment were fed to the animals in the catchment, and